DE 197 27 186 B4 discloses a pendulum-piston and cylinder arrangement. The pendulum piston is produced integrally together with a connecting rod. A cup seal composed of polytetrafluoroethylene (PTFE) is clamped by means of its leg oriented radially with respect to the piston longitudinal axis between a piston rim and a pressure plate secured on the piston by means of a central screw, while an approximately circular leg bent by approximately 90° and aligned approximately parallel to the piston longitudinal axis provides sealing with respect to a cylinder in which the piston moves backward and forward. The cup seal is supplied for assembly in the shape described having the functional contour of the installed state and is secured in this form on the piston by means of the pressure plate, allowing the piston to be installed in the cylinder with the cup seal. However, resizing of the cup seal before installation in the cylinder is generally required for this purpose. This sizing step leads to increased manufacturing costs.
EP 1 801 416 B1 discloses a reciprocating piston machine, in particular a piston compressor, having a cylinder, a piston running in the cylinder while being sealed off by means of a sealing collar, having a drive motor acting on a crankshaft, the drive shaft of which motor is received by a bore in the crankshaft, and having a connecting rod having a connecting rod shank, at one end of which a connecting rod eye for receiving a crankpin of the crankshaft is formed and on the other end of which the piston formed integrally with the connecting rod is formed. The seal, which is designed as a cup seal, is fixed by means of its leg extending radially in the direction of the piston longitudinal axis, on an encircling shoulder of the piston by means of a press-on ring. The outer contours of the press-on ring and of the piston are of spherical design, in particular being designed as spherical segments.
The press-on ring is required in order firstly to be able to push the relatively stiff sealing collar, which is designed like a closed ring, in an axial direction onto the piston as far as the piston shoulder and then to fix the radially oriented flange on the piston. The press-on ring can be fixed solely by means of a pressing action between the piston and the press-on ring. However, it is also possible, additionally or exclusively, to adhesively bond the press-on ring to the piston or to weld it to the piston, in particular by ultrasonic welding, if the press-on ring and the piston are composed of plastic. Particularly in the case of a piston made of plastic, problems often occur in practice with the pressure between the piston and the press-on ring, which are made from different materials for example, e.g. a metal press-on ring and a piston made of plastic, or in the case of a press-on ring and a piston made of plastic owing to the inadequate pressing action due to the flowing effect of the plastic. An adhesive bond between the press-on ring and the piston poses demanding requirements on the cleanliness of the production process, does not have a very high process reliability and gives rise to increased costs. This also applies to welding the press-on ring to the piston.